Time-dependent taphonomic site loss leads to spatial averaging: implications for archaeological cultures

Abstract

Archaeologists typically define cultural areas on the basis of similarities between the types of material culture present in sites. The similarity is assessed in order of discovery, with newer sites being evaluated against older ones. Despite evidence for historical winnowing where the number of discoverable sites declines with increased time depth due to taphonomic bias, little attention has been paid to how this impacts archaeological interpretations about the spatial extents of material culture similarity. This paper tests the hypothesis that spatial averaging as a result of spatially incomplete datasets results in larger regions of similarity. In order to avoid assumptions of cultural processes, we apply subsampling algorithms to a naturally occurring, spatially distributed dataset of soil types. We calculate how distances to the minimum values in similarity between data points change as smaller percentages of the total dataset are used to construct distance decay curves. We show that there is a negative relationship between the percentage of points used to evaluate similarity across space and the absolute distances to the first minimum in similarity for soil classifications at multiple spatial scales. This negative relationship indicates that incomplete spatial datasets lead to an overestimation of the area over which things are similar. Moreover, the location of the point from which the calculation begins can determine the size of the region of similarity. This has important implications for how we interpret the spatial extent of similarity in material culture over large distances in prehistory.